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2822
ADVANCED SUBSIDIARY GCE
PHYSICS A
Electrons and Photons
FRIDAY 11 JANUARY 2008
Afternoon
Time: 1 hour
*CUP/T27964*
Candidates answer on the question paper.
Additional materials: Electronic calculator
INSTRUCTIONS TO CANDIDATES
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Write your name in capital letters, your Centre Number and Candidate Number in the boxes above.
Use blue or black ink. Pencil may be used for graphs and diagrams only.
Read each question carefully and make sure that you know what you have to do before starting your
answer.
Answer all the questions.
Do not write in the bar codes.
Do not write outside the box bordering each page.
Write your answer to each question in the space provided.
INFORMATION FOR CANDIDATES
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FOR EXAMINER’S USE
The number of marks for each question is given in brackets [ ] at the end
of each question or part question.
The total number of marks for this paper is 60.
You will be awarded marks for the quality of written communication
where this is indicated in the question.
You may use an electronic calculator.
You are advised to show all the steps in any calculations.
Qu.
Max.
1
8
2
9
3
9
4
7
5
12
6
15
TOTAL
60
Mark
This document consists of 15 printed pages and 1 blank page.
SP (SM/CGW) T27964/11
© OCR 2008 [T/100/3701]
OCR is an exempt Charity
[Turn over
2
Data
speed of light in free space,
c = 3.00 × 10 8 m s –1
permeability of free space,
0 = 4 × 10 –7 H m–1
permittivity of free space,
0 = 8.85 × 10 –12 F m–1
elementary charge,
e = 1.60 × 10 –19 C
the Planck constant,
h = 6.63 × 10 –34 J s
unified atomic mass constant,
u = 1.66 × 10 –27 kg
rest mass of electron,
me = 9.11 × 10 –31 kg
rest mass of proton,
mp = 1.67 × 10 –27 kg
molar gas constant,
the Avogadro constant,
R = 8.31 J K –1 mol –1
NA = 6.02 × 10 23 mol –1
gravitational constant,
G = 6.67 × 10 –11 N m 2 kg –2
acceleration of free fall,
g = 9.81 m s –2
© OCR 2008
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Formulae
uniformly accelerated motion,
s = ut +
1
2
at 2
v 2 = u 2 + 2as
1
sin C
refractive index,
n=
capacitors in series,
1
1
1
+
+...
=
C C1 C2
capacitors in parallel,
C = C1 + C2 + . . .
capacitor discharge,
x = x0e–t/CR
pressure of an ideal gas,
p=
radioactive decay,
x = x0e– λt
1
3
Nm 2
<c >
V
t = 0.693
λ
critical density of matter in the Universe,
relativity factor,
3H02
ρ0 =
8G
= √ (1 –
current,
I = nAve
nuclear radius,
r = r0A1/3
sound intensity level,
© OCR 2008
= 10 lg
v2
)
c2
( )
I
I0
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Answer all the questions.
1
A cell, a resistor of resistance 120 Ω and a negative temperature coefficient (NTC) thermistor are
connected in series.
(a) In the space below, sketch a circuit diagram of this arrangement.
[2]
(b) The cell has e.m.f. 1.4 V and negligible internal resistance. At a particular temperature, the
current in the resistor is 5.0 × 10–3 A.
(i)
Calculate the potential difference across the resistor.
potential difference = ……………………………. V [2]
(ii)
Calculate the resistance of the thermistor at this temperature.
resistance = ……………………………. Ω [2]
(c) State and explain how the potential difference across the resistor changes when the
temperature of the thermistor is lower.
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[Total: 8]
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BLANK PAGE
PLEASE DO NOT WRITE ON THIS PAGE
© OCR 2008
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2
(a) Draw a line from each of the named components on the left-hand side to the correct I-V
characteristic on the right-hand side.
I
metallic wire at constant temperature
0
0
V
I
semiconductor diode
0
0
V
I
filament lamp
0
0
V
[1]
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(b) In this question, two marks are available for the quality of written communication.
Explain, in terms of resistance, the shape of the I-V graph for each component below.
(i)
Metallic wire at constant temperature.
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(ii)
Semiconductor diode.
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(iii)
Filament lamp.
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[6]
Quality of Written Communication [2]
[Total: 9]
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8
3
(a) State one similarity between potential difference and electromotive force.
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(b) Define the volt.
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(c) (i)
Define the kilowatt-hour (kW h).
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(ii)
Determine the value of the kilowatt-hour in joules.
1 kW h = ……………………………… J [1]
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9
(d) A d.c. supply is connected across a variable resistor. The resistance of the variable resistor
is changed. Fig. 3.1 shows the variation of the power P dissipated in the resistance R of the
variable resistor.
5
P/W
4
3
2
1
0
0
2
4
6
8
R/Ω
10
12
Fig. 3.1
(i)
Use Fig. 3.1 to determine the potential difference across the variable resistor when it
dissipates maximum power.
potential difference = ……………………………. V [3]
(ii)
Explain why your answer to (i) is not equal to the e.m.f. of the supply.
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[Total: 9]
© OCR 2008
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10
4
Fig. 4.1 shows a section through a loudspeaker.
cone
N
circular coil
S S
N
magnet
Fig. 4.1
The circular coil is free to move up and down in the space between the North and South poles of the
magnet. The coil is connected to a d.c. supply of e.m.f. 1.5 V and of negligible internal resistance.
(a) On Fig. 4.1, draw arrows to show the directions of the magnetic field between the poles of the
magnet.
[1]
(b) The length of the wire in the coil is 24 m and its resistance is 8.0 Ω. The magnetic flux density
of the magnetic field at the position of the coil is 1.2 × 10–2 T. Calculate the force experienced
by the wire in the coil due to the magnetic field.
force = ……………………………. unit ………. [4]
(c) Wire of the same length and material but half the diameter of the original wire is used to make
a similar coil. State and explain the change to your answer to (b) when this coil is used in
place of the original one.
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[Total: 7]
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5
(a) State Ohm’s law.
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(b) From the list below, circle the quantity that is conserved in Kirchhoff’s second law.
charge
e.m.f.
energy
time
[1]
(c) Fig. 5.1 shows an electrical circuit.
R
E
2R
Fig. 5.1
The battery has e.m.f. E and negligible internal resistance. The resistances of the resistors
are R and 2R. Calculate
(i)
the total resistance of the circuit in terms of R
resistance = ………………………[2]
(ii)
the current from the battery in terms of E and R.
current = ……………………………..[1]
© OCR 2008
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(d) Fig. 5.2 shows a circuit.
12 Ω
0.16 A
0.48 A
18 Ω
E
36 Ω
I
Fig. 5.2
The battery has negligible internal resistance.
Determine
(i)
the charge passing through the battery in a time of 150 s
charge = …………………………. C [2]
(ii)
the number of electrons responsible for the charge in (i)
number = ……………………………[1]
(iii)
the current I in the 18 Ω resistor
current = ………………….. A [1]
© OCR 2008
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(iv)
the e.m.f. E of the battery.
e.m.f. = ………………………………… V [2]
[Total: 12]
Please turn over for question 6.
© OCR 2008
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6
(a) State one main property of an electromagnetic wave.
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...............................................................................................................................................[1]
(b) Arrange the following electromagnetic radiations in the order of increasing wavelengths.
Start with the shortest wavelength.
infrared
visible light
gamma rays
microwaves
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(c) The table below shows the work function energies of some metals.
metal
(i)
work function energy
(eV)
beryllium
5.0
magnesium
3.7
potassium
2.3
silver
4.7
zinc
4.3
Define the work function energy of a metal.
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(ii)
State and explain which metal has the lowest threshold frequency.
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© OCR 2008
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(iii)
A plate made of magnesium is illuminated with electromagnetic waves of wavelength
3.2 × 10–7 m. The electrons emitted from the surface of the plate have a range of kinetic
energies.
1
Describe how the incident radiation interacts with the metal to release electrons
from its surface and explain why these electrons are emitted with a range of kinetic
energies.
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2
Show that the maximum kinetic energy of the electrons emitted from the surface of
the magnesium plate is 3.0 × 10–20 J.
[3]
3
Calculate the de Broglie wavelength of an electron emitted with maximum kinetic
energy.
wavelength = ………………………….. m [3]
[Total: 15]
END OF QUESTION PAPER
© OCR 2008
16
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